Unless otherwise specifically provided for by statute, a person with a mental illness shall be admitted to a hospital as an in-patient only pursuant to the provisions of this article, except that chemically dependent patients may be admitted to chemical dependence facilities operated by such hospitals under contract or agreement with the office of alcoholism and substance abuse services in accordance with the provisions of article twenty-two of this chapter. The section of the mental hygiene law under which a patient is admitted or under which any change of legal status is subsequently effected shall be stated in the patient's record.